1. Field of the Invention
This invention generally relates to semiconductor manufacturing equipment and, more particularly, to a method of manufacturing a semiconductor device with a SOI structure.
2. Related Art
A silicon-on-insulator (“SOI”) structure includes an active silicon layer on an electrically insulating silicon oxide layer. The creation of SOI wafers represents an intermediate step between the fabrication of the polished, bulk wafers and the creation of electronic components.
Semiconductor manufacturers can fabricate integrated circuits (ICs or chips) on the top layer of the SOI wafers using the same processes used on plain silicon wafers. The embedded layer of insulation enables the SOI-based chips to function at significantly higher speeds while reducing electrical losses. The result is an increase in performance and a reduction in power consumption.
Many methods have been provided related to the formation of an oxide layer on a surface of a silicon substrate. One such method, known as a hydrogen ion separation process, is described below with reference to FIGS. 1A-1F.
As illustrated in FIGS. 1A and 1B, a silicon substrate 100 and a support substrate 102 are provided. A silicon dioxide (SiO2) layer 104 is grown or otherwise formed on silicon substrate 100 to create an insulating film. Generally, SiO2 layer 104 is formed to have a thickness required for fabrication of a device on an SOI substrate.
FIG. 1C illustrates a hydrogen implantation 106 into silicon substrate 100 through SiO2 layer 104. The implanted hydrogen ions break bonds between silicon atoms in the silicon crystal, and terminates non-bonded bands of silicon atoms.
As illustrated in FIG. 1D, in the next step of the process, silicon substrate 100 is turned upside down and laid on top of support substrate 102 so that the surface of silicon substrate 100 nearest to hydrogen implantation 106 is in direct contact with support substrate 102. Thereafter, silicon substrate 100 and support substrate 102 are bonded together at the contacting surfaces to form a combined structure 108. Once the combined structure 108 is complete, it is subjected to a relatively low temperature heat treatment in the range of about 300° C. to about 800° C.
As the temperature rises hydrogen implantation 106 is agglomerated at a plane defined at the depth of hydrogen implantation 106, which is parallel to a surface of silicon substrate 100. As shown in FIG. 1E, since support substrate 102 makes close contact with silicon substrate 100 with SiO2 layer 104 sandwiched therebetween, silicon substrate 100 is separated into two pieces partially due to the force of deformation caused by a difference in the thermal expansion coefficient between support substrate 102, and SiO2 layer 104 and partially due to the agglomeration of hydrogen implantation 106. In the separation of silicon substrate 100, one separated piece remains silicon substrate 100 and the other piece 109 remains bonded to support substrate 102 with SiO2 layer 104 therebetween. The separated piece acts as an SOI active layer 110.
As shown in FIG. 1F, the completed SOI substrate 112, including the SOI active layer 110 can be subjected to a second heat treatment at a relatively high temperature, specifically, at about 1000° C. or greater. The second heat treatment is provided to enhance and ensure that an efficient bonding force is applied between support substrate 100 and SiO2 layer 104.
Unfortunately, the force of deformation caused by the difference in the thermal expansion coefficient of support substrate 102 and SiO2 layer 104 can subject the SOI structure to stresses which cause the structure to break, shatter or become otherwise unusable.
Increasing the time for conducting heat treatments may help to reduce the stress effects, however, processing times are already approaching unreasonable durations. For example, for a bonded together SiO2 layered substrate and a support substrate subjected to a heat treatment at 800° C., the heat treatment lasts for about 10 minutes. When the heat treatment is carried out at 300° C., the heat treatment time extends to about 24 hours.
When support substrates are made of different materials from the silicon substrate, such as in a silicon-on-quartz (SOQ) substrate or other silicon-on-foreign (SOF) substrate, the need to lower heat treatment temperatures increases, since the effect of the difference of the thermal expansion coefficient of the different materials becomes more pronounced.
What is needed is a method for heat treating SOI structures with varying types of support substrates without causing breakage of the SOI structure or requiring slow production rates.